Gas-operated firearms utilize a portion of the high-pressure gas resulting from the discharge of a cartridge to cycle the action of the firearm. The portion of high-pressure gas typically exits via a port in the barrel, and subsequently impinges on the surface of a piston head. Resulting movement of the piston unlocks the action, extracts the spent case from the chamber, ejects the spent case from the firearm, cocks the hammer, chambers a fresh cartridge from a magazine, and locks the action.
The high-pressure gas must be regulated to avoid either excessive or inadequate pressure. Excessive pressure generates unwanted wear and potential damage to components, if the energy is well more than that needed to cycle the action. Inadequate pressure may be insufficient to cycle the action, and generate malfunctions. Normally, a firearm is designed for a given application, such as a certain type of ammunition and certain accessories (such as a sound suppressor or lack thereof) within a suitable operating range for that application. However, when users wish to change some aspect of the application, they may face major tasks to modify or replace major components on their rifle to provide a suitable gas flow. Various methods have been used, including tuning the gas port size, adjusting the mass of the operating parts, and changing spring characteristics to prevent overly violent (or inadequate) movement of the action. While these traditional approaches are effective at controlling movement of the action, the use of a sound suppressor or specialized ammunition with a firearm can result in excessive gas pressure that accelerates wear and adversely affects accuracy. While some firearms have gas blocks that can be replaced with alternatives that reduce the gas pressure, some firearms have permanently-mounted gas blocks or gas blocks that are difficult to remove.
Therefore, a need exists for a new and improved piston for a gas-operated firearm that enables the user to easily adjust the gas pressure applied to the action components of the firearm. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the piston for a gas-operated firearm according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of enabling the user to easily adjust the gas pressure applied to the action components of the firearm.